In a typical aircraft electric power generation and distribution system, for which the instant invention is particularly suited, it is required that electric power generated by multiple power sources be effectively distributed to provide power to multiple electrical loads.
The power sources typically include one or more primary generators operatively connected to be driven by the propulsion engines, an auxiliary generator driven by a small gas turbine, emergency generators driven by an emergency power unit turbine, or by a ram air turbine and one or more batteries. One or more external power connectors are also typically required to provide electric power to at least a portion of the electrical loads during periods when the aircraft is on the ground and the propulsion engines are shut down.
The type of electrical loads for a given aircraft will vary, depending particularly on whether the aircraft is a military fighter type aircraft or a commercial airliner. In general, however, virtually all modern aircraft, whether military or commercial, have a number of flight critical loads such as avionic equipment required for communication and navigation, electromechanical actuation equipment required for manipulation of flight control surfaces, and electric motor driven fuel pumps and control valves. Additional electrical load equipment for environmental control, de-icing, and lighting is also usually required. Military aircraft also require electric power for weaponry, fire control radars and computers, and electronic warfare equipment. Commercial aircraft also require additional electric power for passenger comfort equipment such as galleys and lavatories.
In general, during normal flight operations, virtually all of the electric power required by the aircraft is supplied by the primary generators, augmented during takeoff and landing operations by the auxiliary generator. When the aircraft is on the ground, power is typically supplied by the auxiliary generator or from ground service carts by means of the external power connectors. Should an emergency condition occur during flight, such as the loss of a propulsion engine, the various auxiliary, emergency, and battery power sources are utilized to provide electric power to at least certain flight critical loads which allow the aircraft to be safely maneuvered until the engine can be re-started or safely landed with the propulsion engine nonoperative.
From the foregoing, it will be appreciated that the electric power generation and distribution system of a modern aircraft is quite complex and, of necessity, includes a high degree of redundancy and flexibility to allow operation of the aircraft in a variety of normal and emergency operational modes, both in flight and on the ground. It will also be appreciated that some means of selectively interconnecting-the various power sources and loads, and means for sensing and controlling the configuration of the electric power system, must be provided if the inherent flexibility and redundancy of the electric power system are to be effectively utilized.
Since the various power sources and loads are physically distributed throughout the aircraft, such means for selectively interconnecting is typically provided by a network of feeder cables and wires emanating from the sources and loads and interconnected at various points by switching or protective devices such as contactors, remotely controllable circuit breakers, or fuses. In order that the electric power system may be reconfigured to suit various operational modes, it is customary to provide one or more common connection points, known as load buses, to which the various power sources and loads may be attached. It is also customary where multiple load buses are utilized to provide a tie bus such that the individual load buses may be interconnected in a variety of configurations to allow further flexibility and redundancy in the electric power system.
With such a complex and flexible electric power system, some means of automatically monitoring both the configuration and the health of the system, as well as means for controlling the various interconnections, must be provided to avoid overburdening the pilot and crew of the aircraft. It is customary, therefore, to provide a control circuit having multiple current sensing devices, such as current transformers (CTs), which sense a flow of electric current in the various feeders and wires and provide this information to control units, such as generator control units (GCU) or bus control units (BCU) which are electrically connected to receive additional input regarding desired system configuration from the flight deck and further electrically connected to open or close the various contactors and remotely controllable circuit breakers of the electric power system. U.S. Pat. Nos. 4,321,645 and 4,403,292, assigned to the assignee of the instant invention, provide further details of both the construction and operation of such means for monitoring and controlling an aircraft electric power system.
In the past, it has been customary to route the various feeder cables and wires through the aircraft structure to a centralized electric power center (EPC) in which the various switching and sensing devices, such as the various contactors, circuit breakers, fuses, and sensors used for interconnecting the power sources and loads, were co-located. Customarily, the various switching, protection, and sensing devices have been discrete components mounted on a wall or other structure within the electric power center (EPC) and electrically interconnected by wires and cables. This approach provided significant advantages in that the switching and sensing devices could be commonly used in different aircraft electric power systems by simply changing the interconnecting wires and cables within the electric power center.
The common electric power center approach also has significant disadvantages, however. Such electric power centers are physically quite large to allow room for the interconnecting wires and cables which are typically large in diameter to carry the required current without overheating and therefore relatively inflexible, thereby requiring large bend radii. Such electric power centers are also highly labor intensive and therefore expensive to assemble, with the electric power center for a typical three-engine commercial airliner requiring as much as 500 man hours of skilled labor to complete final assembly. Since the interconnecting wires and cables are large and inflexible, their length must be tightly toleranced, thereby driving up the cost. Maintenance and repair are often difficult since a large number of wires may need to be sequentially removed and replaced in order to gain access to and replace a failed component.
While the customary approach of grouping the interconnecting wires, cables, switching and sensing components together in a central location does facilitate interconnection, there are costs and, in some cases, additional safety risks involved. As previously described, centralized EPCs utilizing discrete components connected by wires and cables are large and must, therefore, typically be located in large spaces suitable for more productive uses such as a cargo bay, thereby occupying valuable space within the pressurized envelope of the aircraft, instead of other presently non-utilized small spaces within and outside the pressurized envelope. Additionally, with all electric power on the aircraft concentrated within a single EPC, great care must be taken in the design and operation of the aircraft such that a single event, such as a component failure within the EPC, an engine disintegration, or detonation of an explosive device on board the aircraft, cannot cause a total loss of electric power.
The instant invention is directed to overcoming one or more of the aforementioned problems and disadvantages.